Motion Sensor and compact fluorescent bulbs

Discussion in 'Electrical Forum discussion & Blog' started by paulsiu, Aug 25, 2009.

  1. paulsiu

    paulsiu New Member

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    Jun 18, 2009
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    Itasca, IL
    The light on my ceiling light burnt out, so I replaced it with a compact flourescent. Much to my surprise, it did not work as I expected. The light is hooked up to a motion sensor and when the bulb doesn't turn off. It instead glows dimly or strobes.

    Is there a incompatibility issue with montion sensor and compact flourscent? Why is that?

    Since the bulb is glowing dimly, this means a low current is going through the bulb. Does this mean motion sensor actually draws power and so isn't so energy efficient after all?

    Paul
     
  2. jimbo

    jimbo Plumber

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    Aug 31, 2004
    Location:
    San Diego
    For a general rule, compact fluorescent bulbs are NOT compatible with motion sensors or dimmers.

    There are exceptions for dimming: you must get a bulb AND ballast AND dimmer which are ALL rated for dimming. The bulbs will more expensive, and the dimmer will run over $50.

    Many simple motion sensors like you probalby have work by "stealing" a tiny amount of current when the bulb is off. An incandescent bulb pretty much ignores this. Flourescents tend to glow or flicker. You can get a compatible motion sensor....it will set you back about $50.
     
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  4. leejosepho

    leejosepho DIY scratch-pad engineer

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    disabled-retired industrial fabricator
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    200 miles south of Little Rock
    Sure, and lighted switches do the same ...

    Sensors and lighted switches are tools that can *facilitate* efficiency, and they do that as efficiently as possible by consuming a minimum amount of energy necessary. An exception, I believe, would be an "energy-free" sensor for a night light, but even that kind of sensor needs energy from the sun (or from some other source) to hold the circuit open and keep the light off until darkness again takes over.
     
  5. drick

    drick In the Trades

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    May 16, 2008
    Of course it draws power - so does anything that is actively monitoring for an event to happen. Your smoke detectors constantly draw power looking for smoke, your tv constantly draws power looking for the remote, your garage door opener, your furnace.... They draw only a small fraction of what they do when they are on, but they still draw power. I think standby losses account for something like 7-10 percent of all power consumed in the average home. Yes you will save more $$ by not using a motion sensor and never turning on the light. However if you want the light on for just 5 minutes when you get home at night the motion sensor will save you $$$ over leaving the lights on all day or using a timer.

    The reason the CFL won't work is that the motion sensor you have uses the filament in the bulb as a wire to pass a small amount of current for the motion sensor. The bulb does not light because the amount of current drawn is small and the filament does not heat up enough to generate light. When you replace a standard bulb, which is essentially a resistor with a CFL, which is essentially an electronic circuit, either the motion sensor or the bulb or both will fail to work properly. This is because the electronics in the CFL will not pass current in a predictable way, thus causing the results you see.

    They do make motion sensors that work with CFLs, but why bother. The motion sensor turns on the light the minute you need it and CFLs take another minute to warm up to full brightness. By then you probably don't need the light any more. Also CFLs don't like to be repeatedly turned on for short durations. This reduces their life. They want to be on for at least 20 minutes at a time on average.

    -rick
     
  6. paulsiu

    paulsiu New Member

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    Jun 18, 2009
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    Itasca, IL
    Thank you everyone for the explanation. I knew it would be something simple, but there are few explanation when I google.
     
  7. johncap523

    johncap523 New Member

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    Jan 19, 2009
    Well, I just rigged a CFL-approved (by their package anyway) motion sensor to a closet light with a CFL bulb and am also getting the glow described above. Initially the bulb was flickering lightly but that stopped. It also is not as bright in auto on mode as in manual on mode. The QUESTION is, does a CFL-rated dimmer or motion sensor also require dimmable bulbs? The second question is why is this all so damn mysterious? Why can't it all be spelled out clearly so we know what the hell to buy? For example: LED bulbs. One guy tells me they're not dimmable. Another says you need CFL-rated switches. Another says no, any dimmer or switch. It CAN'T be that complicated.

    As for the comment about it needing to warm up longer than the time needed for the light... In this case I don't see that as an issue. CFL flood lights I just installed in the kitchen do take 30 seconds to warm up, but this bulb doesn't seem to need any real time to get to full bright (except as mentioned that it is slightly dimmer in auto on mode than manual). PS- the reason for motion sensors is because my wife loves turning on lights but hates turning them off! So I'm putting one in the master bedroom closet (where the idiot electrician put the switch IN the closet), the laundry room and the garage, all places where the switches are in the room so I can't insall switches with monitors to know from outside the affected room that a light was left on. A slight penalty in brightness in any of those rooms means little. I WOULD, however, prefer to use CFLs on principle if nothing else.
     
  8. jimbo

    jimbo Plumber

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    Aug 31, 2004
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    San Diego
    It is a minefield. Generally, a motion sensor or dusk-to-dawn sensor needs to be a 3 wire device, not a two wire. Besides that, you do need to read the manufacturers specs carefully. Some devices will be compatible with magnetic ballasts, but NOT electronic ballast. Integrated CFL are generally an electronic ballast.

    LED is a whole new ball game. Many of those need special power modules and special dimming controls. At home, I have opted for SWITCHES. I turn the lights on, and turn them off. If I need more light, I turn on ANOTHER one!
     
  9. ballvalve

    ballvalve General Engineering Contractor

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    northfork, california
    I have had a long run of many cfl's on a yard for years. I use the 3 wire sensor from a standard 10$ outdoor motion sensor, and not a drop of glow for me! Its strictly on and off.
     
  10. tmleacock

    tmleacock New Member

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    Location:
    Omaha, NE, USA
    Motion Sensor and compact fluorescent bulbs - a solution

    I found that if you are replacing a switch with a motion sensor and want to use CFLs, often you don't have the option of a 3 wire connection (the switch you are replacing only has two wires running to it). However, my circumstance was such that I needed to control a bank of lights with one motion sensor, not just a single bulb.

    So the solution for me was simple. Use all CFLs in the circuit but include just one incandescent bulb so that the motion switch has the trickle current it needs to operate properly.

    Hope this helps anyone trying to control more than one bulb with a motion sensor, wanting it to work, and wanting to use as many CFLs as possible, while at the same time constrained by only 2 wires available in the wall switch box.
     
  11. ballvalve

    ballvalve General Engineering Contractor

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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    Why do mine work fine with the cheapest motion detector made?
     
  12. All_Thumbs_Handyman

    All_Thumbs_Handyman New Member

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    Dec 9, 2011
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    Ontario
    2-Wire Dawn-to-Dusk and Motion Senson in Same Circuit

    Have read the various replies to this thread and I'll chip in my 2 cents worth in the hope it helps someone with a similar problem.

    I have a single 2-wire circuit servicing both the front porch and the lights outside the garage, which is around the corner of the house. I wanted to improve nighttime security and not spend a bundle on electricity.

    The front porch light is first in the run after the switch - I replaced this with a fixture having a built in dawn-to-dusk sensor and put a low Wattage CFL bulb in it.

    I replaced the lights outside the garage with a fixture that has both built-in dawn-to-dusk and motion sensors - after dark the motion sensor becomes activated. These lights only function properly with an incandescent bulb and here I chose to use 100W bulbs because I want maximum illumination and can set the length of time the bulb will remain on to 1, 5 or 10 minutes thereby limiting energy consumption.

    This set up works well – my porch is always illuminated when it is dark using a CFL that draws 15W and if anyone approaches the driveway the 100W bulbs are set to come on for 5 minutes. When not in use there is indeed a faint glow to from the incandescent bulbs.

    The light fixtures used were not expensive and this set up satisfies both the need for security and low energy consumption.
     
  13. DonL

    DonL Jack of all trades Master of one

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    Some motion detectors have a relay controlling the light.

    If yours has a relay, You will normally hear the relay click when motion is detected and the light comes on.
     
  14. btburger

    btburger New Member

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    Sep 24, 2015
    Location:
    Seattle, Washington
    So if I use a LED bulb on my porch fixture which is controlled by a photo sensor, what's the downside?

    The bulb (Philips SlimStyle LED 10.5w) says it is compatible with dimmers (if they are "leading edge or trailing edge") but not with photo controls, occupancy sensors, or timing devices.

    If it matters, the sensor is separate from the fixture, not integrated with it. But I have no idea how it's wired. I've used CFLs there and they seem to work fine, not glow when off, and last a long time. If the bulb doesn't turn on, flickers, or glows when off, I will just try a different one. But if there's a significant risk of killing the bulb, I won't try it.

    I can understand that motion sensors are a bad idea with bulbs that take time to warm up. But this bulb is instant-on and the photo sensor turns it on just once a day. So that shouldn't be an issue here.

    Thanks!
     
    Last edited: Sep 24, 2015
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    Many of the photo sensors actually never turn off the circuit and use some power running through them to function and may leak some current to the bulb itself. Even when on, some don't provide the full voltage. LED's typically would need some sort of internal power supply, and having some low voltage coming in could cause them to overheat as they try to regulate the voltage. Try putting a 'normal' bulb with a filament in the fixture, then measure the ac voltage between the inlet and the outlet of the photo sensor. Then, try measuring the voltage from the inlet to neutral on both the inlet to it and the outlet. That would give some insight on how the thing works.
     
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Occupation:
    Retired Systems engineer for defense industry.
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    New England
    Many of the photo sensors actually never turn off the circuit and use some power running through them to function and may leak some current to the bulb itself. Even when on, some don't provide the full voltage. LED's typically would need some sort of internal power supply, and having some low voltage coming in could cause them to overheat as they try to regulate the voltage. Try putting a 'normal' bulb with a filament in the fixture, then measure the ac voltage between the inlet and the outlet of the photo sensor. Then, try measuring the voltage from the inlet to neutral on both the inlet to it and the outlet. That would give some insight on how the thing works.
     
  17. Reach4

    Reach4 Well-Known Member

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    IL
    It will not hurt the LED bulb.
     
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